1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in the direction along the surface of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in the direction orthogonal to the surface of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
Like magnetic heads for longitudinal magnetic recording, magnetic heads for perpendicular magnetic recording typically used have a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter called an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The write head comprises a magnetic pole layer that produces a magnetic field in the direction orthogonal to the surface of the recording medium.
For the perpendicular magnetic recording system, it is an improvement in recording medium and an improvement in write head that mainly contributes to an improvement in recording density. It is a reduction in track width and an improvement in write characteristics that is particularly required for the write head to achieve higher recording density. On the other hand, if the track width is reduced, the write characteristics, such as an overwrite property that is a parameter indicating an overwriting capability, are degraded. It is therefore required to achieve better write characteristics as the track width is reduced.
A magnetic head used for a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has a medium facing surface that faces toward a recording medium. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider slightly flies over the surface of the recording medium by means of the airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit centered on the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt called a skew of the magnetic head is created with respect to the tangent of the circular track, in accordance with the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system that exhibits a better capability of writing on a recording medium than the longitudinal magnetic recording system, in particular, if the above-mentioned skew is created, problems arise, such as a phenomenon in which data stored on an adjacent track is erased when data is written on a specific track (that is hereinafter called adjacent track erasing) or unwanted writing is performed between adjacent two tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing between adjacent two tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of a read signal.
A technique is known for preventing the problems resulting from the skew as described above, as disclosed in U.S. Pat. No. 6,504,675 B1, for example. According to this technique, the end face of the pole layer located in the medium facing surface is made to have a shape in which the side located backward along the direction of travel of the recording medium (that is, the side located closer to the air inflow end of the slider) is shorter than the opposite side.
In addition, a magnetic head comprising a pole layer and an auxiliary pole layer is disclosed in U.S. Pat. No. 6,504,675 B1. In the medium facing surface of this magnetic head, an end face of the auxiliary pole layer is located backward of the end face of the pole layer along the direction of travel of the recording medium.
As a magnetic head for perpendicular magnetic recording, a magnetic head comprising the pole layer and a shield is known, as disclosed in U.S. Pat. No. 4,656,546, for example. In the medium facing surface of this magnetic head, an end face of the shield is located forward of the end face of the pole layer along the direction of travel of the recording medium with a specific small space therebetween. Such a magnetic head will be hereinafter called a shield-type head. In the shield-type head the shield has a function of preventing a magnetic flux from reaching the recording medium, the flux being generated from the end face of the pole layer and extending in directions except the direction orthogonal to the surface of the recording medium. In addition, the shield has a function of returning the magnetic flux that has been generated from the end face of the pole layer and has magnetized the recording medium. The shield-type head achieves a further improvement in linear recording density.
U.S. Pat. No. 4,672,493 discloses a magnetic head having such a structure that magnetic layers are respectively provided forward and backward of a middle magnetic layer to be the pole layer along the direction of travel of the recording medium and that coils are respectively provided between the middle magnetic layer and the magnetic layer located forward and between the middle magnetic layer and the magnetic layer located backward. In this magnetic head the two coils are connected to each other in series. According to the magnetic head, it is possible to increase components in the direction orthogonal to the surface of the recording medium among components of the magnetic field generated from an end of the middle magnetic layer closer to the medium facing surface.
Reference is now made to FIG. 15 to describe a basic configuration of the shield-type head. FIG. 15 is a cross-sectional view of the main part of an example of the shield-type head. This shield-type head comprises: a medium facing surface 100 that faces toward a recording medium; a coil 101 for generating a magnetic field corresponding to data to be written on the medium; a pole layer 102 having an end located in the medium facing surface 100, allowing a magnetic flux corresponding to the field generated by the coil 101 to pass, and generating a write magnetic field for writing the data on the medium by means of the perpendicular magnetic recording system; a shield layer 103 having an end located in the medium facing surface 100 and having a portion located away from the medium facing surface 100 and coupled to the pole layer 102; a gap layer 104 provided between the pole layer 102 and the shield layer 103; and an insulting layer 105 covering the coil 101. An insulating layer 106 is disposed around the pole layer 102. The shield layer 103 is covered with a protection layer 107.
In the medium facing surface 100, the end of the shield layer 103 is located forward of the end of the pole layer 102 along the direction T of travel of the recording medium with a specific space created by the thickness of the gap layer 104. At least part of the coil 101 is disposed between the pole layer 102 and the shield layer 103 and insulated from the pole layer 102 and the shield layer 103.
The coil 101 is made of a conductive material such as copper. The pole layer 102 and the shield layer 103 are made of a magnetic material. The gap layer 104 is made of an insulating material such as alumina (Al2O3). The insulating layer 105 is made of photoresist, for example.
In the head of FIG. 15, the gap layer 104 is disposed on the pole layer 102 and the coil 101 is disposed on the gap layer 104. The coil 101 is covered with the insulating layer 105. One of the ends of the insulating layer 105 closer to the medium facing surface 100 is located at a distance from the medium facing surface 100. In the region from the medium facing surface 100 to the end of the insulating layer 105 closer to the medium facing surface 100, the shield layer 103 faces toward the pole layer 102 with the gap layer 104 disposed in between. Throat height TH is the length (height) of the portions of the pole layer 102 and the shield layer 103 facing toward each other with the gap layer 104 disposed in between, the length being taken from the end closer to the medium facing surface 100 to the other end. The throat height TH influences the intensity and distribution of the field generated from the pole layer 102 in the medium facing surface 100.
In the shield-type head as shown in FIG. 15, for example, it is preferred to reduce the throat height TH to improve the overwrite property. It is required that the throat height TH be 0.1 to 0.3 micrometer (μm), for example. When such a small throat height TH is required, the following problem arises in the head of FIG. 15.
In the head of FIG. 15, when the head is operated, there is a possibility that the insulating layer 105 expands due to the heat generated by the coil 101, and the end portion of the shield layer 103 closer to the medium facing surface 100 thereby protrudes. If the throat height TH is small, in particular, the portion of the shield layer 103 located between the insulating layer 105 and the medium facing surface 100 is thin, so that it is more likely that the end portion of the shield layer 103 closer to the medium facing surface 100 protrudes. The protrusion of the end portion of the shield layer 103 when the head is operated induces collision of the slider with the recording medium.
For the shield-type head as shown in FIG. 15, for example, there are some cases in which such a phenomenon noticeably arises that there occurs attenuation of signals written on one or more tracks adjacent to the track that is a target of writing or reading in a wide range along the direction of track width (The phenomenon will be hereinafter called wide-range adjacent track erase). One of possible reasons for the occurrence of the wide-range adjacent track erase in the shield-type head will now be described. The magnetic flux that has been generated from the end face of the pole layer 102 and has magnetized the recording medium returns to the shield layer 103. It is assumed that expansion of the magnetic flux that has been generated from the end face of the pole layer 102 and the magnetic flux returning to the shield layer 103 is one of the reasons for the wide-range adjacent track erase.
According to the magnetic head having the structure disclosed in U.S. Pat. No. 4,672,493, it is possible to increase components in the direction orthogonal to the surface of the recording medium among components of the magnetic field generated from the end of the middle magnetic layer closer to the medium facing surface. Therefore, it is assumed that it is thereby possible to suppress the wide-range adjacent track erase.
The magnetic head having the structure disclosed in U.S. Pat. No. 4,672,493 includes the two coils connected in series to each other. Such a magnetic head including two coils connected in series to each other will be hereinafter called a two-coil head. A magnetic head in which only one coil is provided will be hereinafter called a one-coil head. Problems of the two-coil head will now be described, comparing the one-coil head and the two-coil head with each other. To simplify the comparison between the one-coil head and the two-coil head, it is assumed that the two coils of the two-coil head and the one coil of the one-coil head are all equal in the number of turns and resistance.
In the two-coil head, currents of equal values are respectively fed to the two coils. To make the magnetomotive force of each of the coils of the two-coil head equal to that of the one coil of the one-coil head, it is necessary that the value of the current fed to each of the two coils of the two-coil head be equal to the value of the current fed to the one coil of the one-coil head. Then, the total of heating values of the two coils of the two-coil head is twice the heating value of the one coil of the one-coil head. Consequently, there arises a problem that the possibility of protrusion of a portion of the medium facing surface due to the heat generated by the coils of the two-coil head is greater, compared with the one-coil head.
Another problem of the two-coil head is that, since currents of equal values are respectively fed to the two coils, it is impossible to adjust the magnetomotive force of each of the coils by adjusting the value of the current for each of the coils.